A measurement element including a resistor which constitutes a heater and is thermally insulated from a semiconductor substrate is conventionally known. Such measurement element is formed using a semiconductor thin film formation technique and a micromachining technique.
A diaphragm sensor formed as follows is an example of such measurement element (see Patent Literature 1). Specifically, through anisotropic etching, an opening is formed in a semiconductor substrate at a central part on the back side thereof. The opening has a trapezoidal cross section and does not penetrate the top surface of the semiconductor substrate. Then, a thin-wall diaphragm part is formed on a bottom side of the opening, namely, on a top surface side of the semiconductor substrate. Using the thin film formation technique, a thin-film heater element and a thin-film resistance thermometer element are formed on a central portion of the top surface of the diaphragm part. In this diaphragm sensor, the formation of the diaphragm part allows the diaphragm part to be thermally insulated from the semiconductor substrate. Moreover, in the diaphragm part between the heater element and the resistance thermometer element, a slit part penetrating the diaphragm part is provided. Thereby, thermal conduction from the heater element to the resistance thermometer element is reduced. Multiple slit parts penetrating the diaphragm part are further provided in the diaphragm part between the heater element and a diaphragm periphery part, namely a thick wall part of the semiconductor substrate, and between the resistance thermometer element and the diaphragm periphery part. Thereby, thermal conduction from the heater element and the resistance thermometer elements to the thick wall part of the semiconductor substrate is reduced.
An another example of the measurement element is a heater device (see Patent Literature 2) including a silicon substrate in which a cavity part is formed, a thin film thermally isolated from the silicon substrate by the cavity part, a thermo-sensitive resistor having a thin-film heater and a thin-film temperature sensor formed on the thin film. In this heater device, the cavity part is formed by etching removal of the silicon substrate from a side of the silicon substrate where the thin-film heater and the thin-film temperature sensor are formed, to such a degree that the cavity part does not penetrate the back side of the silicon substrate. The thin film on which the thin-film heater and the thin-film temperature sensor are formed constitutes a bridge part bridging across the cavity part. In such a structure, the cavity part has an opening in the thin film around the bridge part. Patent Literature 2 discloses that a cantilever structure may be employed instead of the bridge part. When the cantilever structure is employed, the cavity part has an opening in the thin film around the cantilever structure part.